Collagen types I, III, IV and V and fibronectin were localized in neurofibromas from six patients with von Recklinghausen's neurofibromatosis (NF) using indirect immunofluorescence (IIF) and peroxidase anti-peroxidase (PAP) techniques. Type I and III collagens were abundantly and rather evenly present in the tumours and formed a continuous network, but were absent from the capillary endothelial walls and were sparse in the perineurium of the occasional nerve fascicles. The type III/type I + type III collagen ratio in neurofibromas varied from 17.4% to 37.3% when estimated with cyanogen bromide peptide analysis. Fibronectin was detected in areas where type I and III collagens were present but was most intensively stained in the vascular walls and perineurium. Type IV collagen was detected at the dermo-epidermal junction of the skin overlying the tumours, in the endothelial cells of the capillaries, the perineurium and endoneurium. Furthermore, in the tumourous stroma there was plenty of type IV collagen appearing as a discontinuous patchy pattern suggesting abundant basement membrane material associated with cells forming the tumours. Type V collagen distribution was very similar to that of type IV collagen.